The present invention relates to composite mica powder and new red synthetic mica to be used as base material for paint, ink, coating agent, plastic, film, fiber, glass, and glaze, and also to an ultraviolet ray screening agent containing said mica powder.
Mica powder is used as a filling material for plastics and paint or as pigment for cosmetic products. Also, a mica product having interference color and with its surface covered with an oxide having high refractive index such as titanium oxide is known as "pearl mica".
On the other hand, as means for screening ultraviolet rays, methods are known such as a method for screening ultraviolet rays by scattering effect of particles and a method to absorb ultraviolet ray energy and to convert it to thermal energy. A typical example of the former is to use titanium oxide, and this is used as an ultraviolet ray scattering agent in cosmetic products, plastics, etc. As the material for the latter, an ultraviolet ray absorbing agent having benzophenone and the like as principal component is known. In addition, a large number of ultraviolet ray screening agents have been proposed. For example, there are composite oxides of metal such as aluminum and zinc (Japanese Patent Laid-Open Publication No. 62-275182), zirconia particle containing cerium (Japanese Patent Laid-Open Publication No. 2-135275), etc. Also, an ultraviolet ray absorbing agent containing mica has also been proposed. For example, there is a product having nickel-containing synthetic mica as main component (Japanese Patent Laid-Open Publication No. 58-19379), a product having synthetic mica containing Te and the like as main component (Japanese Patent Laid-Open Publication No. 3-33179), etc. Also, an ultraviolet ray screening pigment has been proposed (Japanese Patent Laid-Open Publication No. 62-187770), which is covered with titanium oxide in such quantity that pearl luster due to interference does not virtually appear on mica surface.
On the other hand, mica has been widely used for cosmetic products because it has excellent transparent property, luster and high extensibility. In recent years, not only natural mica but also synthetic mica have been developed as an additive for cosmetic products (Japanese Patent Laid-Open Publication No. 63-241072).
The mica powder of a conventional type has been used as scale-like particles of about 1 to 500 .mu.m after being pulverized by a dry or wet type pulverizing method. This conventional type mica powder is disadvantageous in that it can utilize only the heat-resistant and insulating properties of the mica powder. For this reason, the ultraviolet ray absorbing function is provided by giving interference color through adoption of a particle structure covered with titanium oxide as in the case of the pearl mica described above or by a method to replace the elements in mica with other elements through synthesis. However, the pearl mica covered with titanium oxide can give interference color, but it has no transparency specific to mica, or titanium oxide has poor resistance to light. The ultraviolet ray absorbing mica which contains specific elements does not have sufficient effect to screen ultraviolet rays.
In a ultraviolet ray screening agent, the ultraviolet ray scattering agent such as titanium oxide has excellent effect to screen ultraviolet rays while it impairs transparency of mica because it also scatters visible rays, and this is not suitable for the application where transparency is required. In case it is blended in cosmetic products, the white color is exaggerated and gives an unnatural impression. On the other hand, an organic type ultraviolet ray absorbing agent has outstanding ultraviolet ray absorbing potency within a specific wavelength range, but it has poor weatherproof property and lacks stability.
As natural mica, muscovite, phlogopite, and biotite are known, and these are grayish white to blackish brown in color. Mica can be synthesized by various methods, and it is known that mica haring an outstanding white color can be obtained from synthesis and that colored synthetic mica can be produced by coordinating colored elements in the crystal structure.
On the other hand, mica is widely used in cosmetic products because it has a high transparent property, luster and extensibility in use. In recent years, not only natural mica but also synthetic mica has been developed as an additive for cosmetic products. For example, the Japanese Patent Laid-Open Publication No. 63-241072 discloses a synthetic mica powder, in which less fluorine ions are eluted and which has a low surface activity and a high oil impregnation properties.
As described above, mica has not been used widely because color cannot be given to it, and despite of its excellent property, only the properties such as insulating property or leafing property coming from its scale-like shape can be utilized. In the fields of paints, plastics, cosmetic products, etc., there are strong demands on a material, which is red in color and has ultraviolet ray screening effect to improve the durability of organic substances. To give red color, however, it is necessary to add a coloring agent such as an organic dye or iron oxide. Because organic dye has low resistance to light and iron oxide contains particles with high refractive index, it is likely to cause unevenness and impairs the transparency important to cosmetic products. On the other hand, an ultraviolet ray scattering agent such as titanium oxide or an organic type ultraviolet ray absorbing agent are used in cosmetic products to defend against ultraviolet rays. Although an ultraviolet ray scattering agent has excellent effect to screen ultraviolet rays, it also scatters visible rays. This leads to impairment of transparency and causes choking and whitening of cosmetic products. An organil type ultraviolet ray absorbing agent has outstanding ultraviolet ray absorbing potency within a specific wavelength range but has poor weatherproof property.